This invention is directed to semiconductor field-effect transistors, and more particularly, to an n-channel junction field-effect transistor.
The junction field-effect transistor has several characteristics which make it a desirable circuit element in many linear applications. It has extremely high input impedance (and consequently, low input current) and very low noise. Because of these characteristics, the junction field-effect transistors are being used in the input stage of operational amplifiers and comparators. In both types of circuits, it is desirable to have low input currents and low noise. When the gate of the JFET is the input of the amplifier or comparator, very low circuit input currents are achieved (at least at room temperature). The first JFETs used in integrated circuit operational amplifiers and comparators were p-channel devices because initially they were the easiest to integrate along with bipolar circuit elements. However, because of their operating requirements it was not possible to take the inputs of the p-channel JFET input circuits to ground when the circuits were operated from a single power supply. This restricted the common mode range of the circuits.